1. Field of the Invention
The present invention is generally related to a method for selecting the pitch of a controllable pitch marine propeller and, more particularly, to a method for selecting the pitch of a controllable pitch propeller based on a magnitude of an input parameter which is used to select a desired magnitude of an engine operating characteristic as a function of the input parameter, after which the pitch of the controllable pitch marine propeller is selected as a function of changes in the magnitude of the engine operating characteristic.
2. Description of the Prior Art
Conventional propellers used in conjunction with planing watercraft often experience large changes in operating conditions throughout the range of boat speed at which they are operated. These changes in watercraft operating conditions, in turn, cause large variations in the propeller""s torque characteristics as a function of engine speed. Unlike automobiles, watercraft typically do not have multi-speed transmissions that allow the load to be adjusted to match the power characteristics of an associated internal combustion engine, so the engine used in a watercraft must be able to accept many different load changes. In practice, it is typical that the propeller load variations seriously limits engine performance in many common situations, although these variations usually are not sufficient to actually stall or overspeed the engine. The fact that propeller load is different at different boat speeds implies that a propeller which is selected to give optimal performance on one boat speed will differ from another propeller that is chosen for optimal engine performance at a different boat speed. Therefore, performance compromises are inherent in choosing conventional propellers for a planing watercraft. In other words, a conventional propeller chosen for best high speed performance would typically compromise low speed acceleration, and vice versa.
U.S. Pat. No. 4,639,192, which issued to Harrell on Jan. 27, 1987, describes a propeller pitch controlling arrangement having a fuel economizing feature. The arrangement has a fuel economizer feature for use on marine vessels and has a mode selector valve operable to a normal mode and an economizer mode. In the economizer mode, a first pilot signal is transmitted to a path selector valve to establish a first flow path to a propeller pitch servomechanism. A second pilot signal is transmitted from a relay valve when the marine vessel speed drops below a predetermined value. The second pilot signal moves the path selector valve to a second position establishing a second flow path to the propeller pitch servomechanism. A first selected fluid pressure from a regulating valve arrangement mechanically linked to the engine fuel rack, is directed to the propeller pitch servomechanism when the first flow path is established. This first selected fluid path is proportional to the movement of the engine fuel rack. A second selected fluid pressure transmitted from a pitch control valve, is directed to the propeller pitch servomechanism when the second flow path is established.
U.S. Pat. No. 5,415,523, which issued to Muller on May 16, 1995, describes a control system for a variable pitch boat propeller. A marine drive is provided with a propeller that is rotatable about a drive axis and has a plurality of blades. The blades are pivotable about respective blade axes projecting generally radially from the drive axis and each blade is movable between a low pitch end position extending generally parallel to a plane perpendicular to the drive axis and a high pitch end position extending at a large acute angle to the plane.
U.S. Pat. No. 4,744,727, which issued to Muller on May 17, 1988, describes a controllable pitch propeller and watercraft drive. The propeller assembly has an inner housing attached to a main driveshaft, the housing having rails on the outer surface thereof. Modules carrying the propeller blades are mounted positively on the rails, with each module having a housing receiving a hub cylinder and bushings axially aligned at opposite sides thereof. Each pair of bushings receives an adjusting piston having an adjusting pin which engages a groove forming a control path in a propeller hub. Each blade is adjusted by a control lever which adjusts each adjusting piston through a mechanical linkage including an adjusting sleeve and a thrust bearing and flange. The hub is provided with open spaces formed between the inner and outer housings to create exhaust ducts through the hub.
U.S. Pat. No. 5,174,718, which issued to Lampeter et al on Dec. 29, 1992, describes a blade pitch change control system. The system is used for adjusting the pitch of a variable pitch propeller blade operatively connected for pitch change to a pitch change actuator piston. A pitch change control system is operatively connected to the pitch change actuator piston for selectively pressuring the pitch change actuator piston to effectuate a desired change in the pitch of the propeller blades.
U.S. Pat. No. 5,226,844, which issued to Muller on Jul. 13, 1993, describes an actuator for a variable pitch propeller. It describes a drive for a boat which has a propeller hub rotatable about a main axis extending in a normal travel direction, a plurality of blades projecting generally radially from the main axis of the hub, and each blade being pivotal so as to be of variable pitch, with respective blade rods extending axially and displaceable axially relative to the hub to vary the pitch of the blades. A stator carried on the boat downstream in the direction from the hub and nonrotatable about the axis rotatably supports a cylinder housing that is releasably connected to the rods for joint axial movement therewith.
U.S. Pat. No. 4,347,039, which issued to Houghton on Aug. 31, 1982, describes a variable pitch screw propeller. The propeller has a crank arm attached to the shaft of each propeller blade and a telescoping drive arm having one end pivotally attached to the propeller hub and the other end pivotally attached to a control rod. The telescoping arm rotates the crank arm to adjust the pitch of the propeller blades to an angle substantially greater than 90 degrees as the control rod is moved longitudinally along a longitudinal axis of the hub of the propeller.
U.S. Pat. No. 4,533,296, which issued to Duchesneau et al on Aug. 6, 1985, describes a pitch control system for a variable pitch propeller. The control system has a mechanical low pitch stop which includes an electrical backup. The backup comprises an electrically operable means to effect blade pitch adjustment toward feather under conditions of failure of low pitch stop indicated by propeller operation at pitch angles in the range of beta operation, but power settings in the range of normal engine speed governor pitch control. Such operating conditions actuate a pair of switches connecting the means to a voltage source to increase blade pitch toward feather, thereby preventing overspeed operation of the propeller.
U.S. Pat. No. 4,599,043, which issued to Muller on Jul. 8, 1986, describes a controllable pitch propeller and watercraft drive. The propeller assembly has an inner housing attached to a main driveshaft, the housing having rails on the outer surface thereof. Modules carrying the propeller blades are positively mounted on the rails, each module having a housing receiving a hub cylinder and bushings axially aligned at opposite sides thereof. Each pair of bushings receives an adjusting piston having an adjusting pin which engages a groove forming a control path in a propeller hub. Each blade is adjusted by a control lever which adjusts each adjusting piston through a mechanical linkage including an adjusting sleeve and a thrust bearing and flange.
U.S. Pat. No. 4,880,402, which issued to Muller on Nov. 14, 1989, describes a method and apparatus for preventing the attachment of foreign bodies to controllable pitch propeller linkages of watercraft. The watercraft has a rotatable propeller drive shaft connected to a driving engine. A coupling is slidably disposed along the shaft. The coupling has a rotatable first section secured to the shaft and a non-rotatable second section spaced from the shaft with a bearing arrangement in which the first section is rotatably disposed. A variable pitch propeller has a hub secured to the shaft. A plurality of propeller blades are rotatably disposed in bearing housings to the hub. Connecting rods are slidably disposed in the bearing housings. Each connecting rod has a position of protection at which it is disposed completely in the corresponding bearing housing wherein it cannot be attacked by foreign bodies.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
An article, titled xe2x80x9cApplication of Modern Digital Controls to Improve the Operational Efficiency of Controllable Pitch Propellersxe2x80x9d by Robert A. Morvillo, was published in SNAME Transactions, Vol. 104, in 1996, at pp. 115-136. This article, describes control systems designs intended for use with fishing trawlers, Great Lakes Bulk Carriers, and a Hopper Dredge. It discusses the applications of a state of the art electronic control system that further exploits the capabilities of controllable pitch propellers. In contrast to a fixed pitch propeller, where the propeller thrust is a function of the only independent variable, shaft rotational speed, the controllable pitch propeller has infinite combinations of pitch and engine speed for a given thrust requirement. This paper considers the design of a robust, multi-parameter propulsion control system with the ability to determine the ideal pitch and engine speed combination in real time for varying operating conditions. Because the design goals of the control system are optimum fuel economy as well as the usual stability and response criteria of most control systems, a steady state model combining the characteristics of the propeller, hull, and prime mover is discussed. In addition, the paper provides a dynamic analysis to ensure acceptable stability and response characteristics of the control system.
Planing watercraft experience wide ranges of conditions under which they are expected to operate. For example, if a planing watercraft is accelerated from a standstill position to a planing condition at wide open throttle, optimum performance of the watercraft requires that it exhibit sufficient acceleration to move the watercraft from a standstill to a speed that is able to achieve planing of the watercraft. Once on plane, the propulsion system must be adequate to increase the speed in an efficient manner to obtain the maximum speed of the watercraft on plane when the engine is operated at wide open throttle.
It would be significantly beneficial if a control system could be provided that allows efficient selection of pitch, in a dynamic manner, that maximizes the performance of the engine of the watercraft as the watercraft experiences a wide variety of operating conditions.
A method for selecting the pitch of a controllable pitch marine propeller of a planing watercraft, in accordance with a preferred embodiment of the present invention, comprises the step of determining a magnitude of an input parameter. The input parameter, in a particularly preferred embodiment of the present invention, is a manually controlled input parameter such as a throttle lever position or a throttle plate position. The method further comprises the step of selecting a desired magnitude of an engine operating characteristic as a function of the input parameter. The engine operating characteristic in a preferred embodiment is engine speed, measured in revolutions per minute (RPM). The desired magnitude of the engine operating characteristic, or engine speed, can be selected from a lookup table as a function of the input parameter, or manually controlled throttle lever. The method of the present invention further comprises the step of measuring an actual magnitude of the engine operating characteristic, such as engine speed. The present invention also comprises the step of determining a desired change in the pitch of the controllable pitch propeller as a function of the difference between the desired magnitude of the engine operating characteristic and the actual magnitude of the engine operating characteristic. In other words, if the input parameter indicates a desired engine speed that differs from the measured actual engine speed, the desired change in pitch would be determined as a function of that difference between the desired and actual magnitudes of the engine speed.
The present invention, as part of the method for selecting the pitch of the controllable pitch marine propeller, can further comprise the step of causing the controllable pitch propeller to experience the desired change in the pitch. This would normally be done with a pitch controller mechanism which is dedicated to receiving pitch position commands from external components and implementing the pitch commands. Alternatively, the actual implementation of the pitch command can be controlled directly by an engine control unit which is the same component used to select the direction in magnitude of the pitch change as a function of the difference between the desired and actual engine operating condition, such as engine speed.
The method of the present invention can further comprise the step of measuring the actual magnitude of the pitch of the controllable pitch marine propeller and adding the desired change in the pitch of the controllable pitch propeller to the actual magnitude of the pitch in order to determine a desired pitch. The method can further comprise the step of causing the controllable pitch propeller to experience the desired change in the pitch, wherein the causing step causes the propeller to move directly to a position which satisfies the desired pitch of the controllable pitch marine propeller. It should be understood, however, that an alternative implementation of the present invention could comprise the steps of first determining the appropriate direction of a desired pitch change and then incrementally causing the propeller to move in predetermined stages in that desired direction until the engine operating condition achieved the desired magnitude. The precise method for implementing the pitch change is not limiting to, the present invention.